Our Nutrition Ignorance

The June Skeptical Inquirerreviews what little we know about nutrition:

Nutrition research and practice have lagged behind many other biological and medical fields. … The data clearly show that much current advice about dietary pyramids, food supplements, megavitamins, and weight loss regimens is frequently unproven, erroneous, or even harmful and is often based on pseudoscience or derivative incorrect professorial opinion. …

A healthy person (given RDA intake of the substances in Table 1) can proceed with a normal (see below), stable weight by eating predominantly fat or carbohydrates or protein or various combinations of these because of the body’s ability to interconvert and utilize carbohydrates, fats, and proteins (amino acids) as needed. In other words, fat, carbohydrate, or protein can serve as the principal source of calories. …

In healthy people who ingest the essential nutrients in Table 1 and have a normal stable weight (BMI approximately 20-25), there is no convincing comparative outcome evidence (as I defined above) that common foodstuffs, e.g., saturated fats like butter, rapidly absorbed carbohydrates like white rice and potatoes, or animal proteins, are especially helpful or harmful. The notion that some diets (e.g., low-fat or low-carbohydrate) are better than others is not based on sound science. …

There is no rigorous scientific evidence for the utility of dietary supplements, including megavitamins in normal-weight (nonpregnant) adults with a stable BMI of 20-25 eating a diet containing adequate amounts of the nutrients in Table 1.

Holding calories constant, a low-fat diet may be no healthier than a high-fat diet. But calories are rarely held constant when most people decide what to eat. I may be just as healthy eating 2000 calories of french fries vs. 2000 calories of salads (assuming all important vitamins, minerals, etc. are consumed in both cases) but, given the huge differences in caloric density, holding the number of calories consumed would probably be fairly difficult.

So maybe the advice is wise, but for false reasons. Fat may be fine by itself, but cutting out fat is a good way to reduce calories while still being able to feel full after a meal.

Fat may be fine by itself, but cutting out fat is a good way to reduce calories while still being able to feel full after a meal.

That’s exactly the sort of plausible-but-wrong hypothesis being talked about in the essay. It’s based on the assumption that “feeling full” versus “feeling hungry” after a meal is entirely a matter of being able to physically sense how “full” the stomach is. Which doesn’t seem to be the case. Unless you’re talking about being so “full” it’s physically painful to eat any more, stomach capacity running out isn’t why people stop eating. Or to turn that around, people don’t, as a rule, eat until stomach capacity runs out. They eat until they are “satisfied”, which most have some inputs based on what’s going on in the bloodstream, or else there would be a better correlation between the calorie density of a society’s diet and that society’s average weight. According to your theory, the Inuit should have all been obese when they were eating a mainly seal- and whale-blubber diet; they weren’t.

John

Maybe I should read the paper more closely, but I didn’t see much evidence that my view is “plausible-but-wrong.” The paper mostly seemed to promote skepticism that this view was correct without providing evidence that the view was actually wrong. Nothing wrong with promoting healthy skepticism, of course, but there’s nothing wrong with suggesting plausible theories (that would ideally be tested later on) either.

And I’d say that the caloric density of a society’s diet might matter a lot, but only for societies that limit their food based on satisfaction, rather than availability. In modern societies, there is really no limit on the number of calories we could eat in a day. Other societies have (and all have previously had) much stricter environmental limits on the number of calories available per day or per person.

On reflection, I thought of two more naive metrics besides stomach-fullness that would fit the bill for the initial (false) theory: Amount of chewing, amount of swallowing.

One big puzzle we have to answer is that weight is surprisingly consistent. If you move or switch jobs such that you’re walking an extra block a day, or if you make a small change in your eating habits, your body just compensates for this automatically somehow. Your appetite and metabolism adjust to the new situation; nobody wastes away or becomes morbidly obese due to the long-term effects of any random 300-calorie change. So we know there’s a feedback loop somewhere in the system, one that reacts not to the *bulk* of the food, not to its density, but to the total amount of energy it contains.

Suppose you are used to eating a certain *amount* per meal. We’ll call that amount X. Whether X is measured in swallows or time chewing or stomach fullness doesn’t matter for our purposes.

Now suppose you switch to a 20% lower calorie-density food. The *first* meal after the change, you still eat X amount of food because that is what were used to – it was the prior equilibrium point. Your calorie intake when consuming amount X was just reduced, so you start losing weight. Second meal, same thing. But eventually something changes. Maybe it takes a day, maybe a week, maybe even longer, but eventually your body *figures out* it’s not getting all the nutrition it used to; some adjustments are made. Your metabolism slows and your hunger level gets increased. And it overshoots a bit; now you gain weight even on the lower-density food because you’re eating more of it and moving less. Within a year or two or five, diet studies tell us you probably weigh more than when you started and have to eat less even to keep your current weight than you did before.

On a personal note, I actually found that adding fat is a good way to reduce calories while still being able to feel full after a meal. But just like subtracting fat, it doesn’t work forever.

ThomasR

Eating too much carbohydrate, especially fructose, messes with the appetite system via the hormones insulin and leptin. As a result the eater isn’t satisfied and goes on to eat more and more calories. This is why so many people are obese. (It can’t happen if one eats meat exclusively.)

Heh. Sceptics love saying this. Did they try under the staircase next door? It would be more honest to say:

“We could find no rigourous scientific evidence…”

(And since all evidence is subject to interpretation, and all interpretation depends on the interpreter’s knowledge and prejudice, this statement does not rule out the ‘rigorous evidence’ having passed right under their noses.)

Robert Koslover

The latest research shows that there are actually only two basic food groups:
1. Chocolates
2. Bacon
Together, these contain the four fundamental nutritional building blocks:
1. Fat
2. Sugar
3. Salt
4. Cholesterol
Symptoms known to arise from insufficent consumption of any of these critical nutrients include cravings and depression.

Robin, on one hand evidence on nutrition is rather unconvincing, on the other hand the null hypothesis that it doesn’t matter what we eat is clearly disproved by the obesity epidemic, and related problems like type 2 diabetes, high blood pressure etc. Something about our modern eating must be wrong.

The main reason there’s not much good evidence seems to be impossibility of running double blind large scale long term trials of nutrition, and huge difficulty of getting even a small subset of these features right in a trial. Animal models are completely useless, and short term human studies pretty close to useless. So lack of solid evidence is unfortunately to be expected.

And due to lack of solid evidence, pretty high impact of nutritional decisions on health, I’d go risk averse and make changes that have decent chance of helping and very low chance of hurting – like limiting sugar intake (average American eats 600kcal of simple sugars a day), taking a multivitamin pill and an omega3 pill every day (on an off chance that I have some deficiency), and weakly preferring less processed and more traditional foods, what fortunately usually means more tasty.

Lifestyle explanations are not entirely implausible, but change in nutrition seems much greater than change in lifestyle. People behave very much like they used to 50 years ago, there is some shift, but there seems to be far too much overlap to explain such drastic shift in incidence of metabolic issues.

On the other hand people’s eating is completely unlike what it was even recently, so this sounds like the most plausible explanation.

Some alternative hypotheses consistent with data are some strange kind of pollution or infection screwing up our hormones and making us fat, but these seem unlikely.

George

Obesity, diabetes and high BP are better than dying young. Since our life expectancy is so high (and increasing) something about our modern eating must be right!

I strongly suspect this will eventually turn out to be like ulcers – there is some environmental cause. Something really weird is going on and we don’t know what it is, but whatever it is is *causing* us to overeat.

I would say the main reason there’s not much good evidence is that people aren’t practicing good science! Taubes made a point of *looking for counterexamples* that might disprove any theory he considered; I wish more people would do that.

By coincidence, I happened to finish reading Good Calories, Bad Calories just last week. Taubes is careful not to claim that low-carb diets are proven to the extent they should be; rather, he shows how attempts to prove the low-fat philosophy have failed despite an absurd amount of government, non-profit, and academic support — the last few pages of Calories are actually a complaint about various studies looking into the safety of low-carb diets, but not their efficacy. The book is an overview of the shenanigans that have gone on in the field of nutritional research over the last hundred years or so.

That said, I agree with Taubes’ conclusion; the best available evidence points to a low-carb diet as the way to lose weight where needed for most people. ThomasR, note the “rigorous” — long-term, well-designed studies are possible and ought to be done. Also note that the article is talking about people that aren’t obese in that section you quoted; there are differences in metabolism that will cause people to react to carbs differently in the Calories story.

Regarding what Calories says, the article posted more or less agrees:

…in obese individuals (BMI > 30), there is some evidence that not only do they eat too many calories but they may also be eating a diet (e.g., rapidly absorbed carbohydrates) that does not “satiate” them and leads to more rapid fat deposition.1 This hypothesis remains to be proven.

….

There is, however, some evidence that low-carbohydrate diets “work” best at least for periods up to one year,22 but this has not been replicated in a two-year study.22a

There is no rigorous scientific evidence for the utility of dietary supplements, including megavitamins in normal-weight (nonpregnant) adults with a stable BMI of 20-25 eating a diet containing adequate amounts of the nutrients in Table 1.

Well, duh. There is also no rigorous scientific evidence for the utility of fire extinguishers in houses that are not on fire.

The whole reason I consume dietary supplements is to compensate for the possibility that I’m *not* getting adequate amounts of the nutrients in Table 1. (And to allow me more leeway in my dietary choices.)

The observation above seems a) completely unsurprising and b) completely irrelevant to any of the reasons why people take dietary supplements.

The problem with diet and nutrition studies is that, for the most part, you can’t have long-term double-blind randomized trials. People know what they’re eating, people don’t stick to a randomly selected diet for very long, and unless monitored, they eat differently than what they admit.

But it seems to me that there is a potentially fruitful source of randomization in the prison system. Say we went to a large state-wide prison system and offered a cash reward to anyone who signed up for a randomized diet trial to last 5 years. Then we randomize who gets what kind of diet, and we put them all in special units so that there’s very little chance of anyone cheating on their assigned diet. It would be somewhat expensive, but not nearly as much as trying to put ordinary civilians under 24/7 monitoring, and the informational benefit would be quite large.

Eric Johnson

Steven Landsburg, while I wouldn’t say your perspective has nothing to it, your indignation won’t survive a look at this:

“Increasing doses of vitamin E were linked to an increase in death,” said lead author Edgar R. Miller, M.D., Ph.D., associate professor of medicine at Johns Hopkins University in Baltimore, Md.

According to the analysis, there is no increased risk of death with a dose of 200 IU per day or less, and there may even be some benefit. However, an increased risk was found at amounts above 200 IU per day and significant risk of death was found starting at 400 IU a day. Those who take greater than 400 IU of vitamin E a day are about 10 percent more likely to die than those who do not, researchers said.

“Many people who take vitamin E supplements take between 400 and 800 IU in a single capsule,” said Miller.

[…]

““Typically, we get about 6-10 IU per day of vitamin E in our diets. […]

These findings parallel the findings of beta carotene supplementation trials. Two major studies showed that beta carotene supplementation results in an increased risk for lung cancer and death. And, as a result, “you will never see beta carotene supplements recommended again,” he said.

I haven’t read the paper and waterboarded its epistemology, cause I don’t really care. Nor have I checked for discordant findings (which so often exist in biomed). All I want to assert is that this viewpoint does exist – moreover, at high levels in the academy.

That appears to be an argument against megavitamins (and specifically megadoses of vitamin E), not against normal multivitamins. For instance, I have a bottle of “One-A-Day Men’s Health Formula” multivitamin in front of me; it claims to include 45 IU (150% of RDA) of Vitamin E, which well below the level that is claimed to be harmful.

Eric Johnson

One vitamin that should be taken by women facing any odds of pregnancy, is folic acid, deficiency in which can promote birth defects. At least that’s the view that my biochem prof at a good university urged on all of us. I’m pretty sure he did say it was a good idea even if you only might become pregnant, which I assume is because some of the effect would take place in the early part of the pregnancy before one is aware of it.

So, there aren’t – according to some, anyway – really solid corpuses of trials to back up idea X or Y about the obesity epidemic. Interesting enough.

But what’s weird to me is this: if the cause is fairly simple, why hasn’t it been discovered, and judged a reliable pivot for obesity normalization, by nonscientists? After all, hasn’t just about everything in the world been tried in attempts to lose weight? And what could possibly be more amenable to amateur study, at least as far as diet, exercise, and other easily obesrved and controlled variables go? Millions of people have tried out enormous numbers of rigid regimes, from the plausible to the wacky, with close attention to the results.